Luminous gas discharge tube



March 12; 1935. H. SOUNDY 1,993,811

LUMINOUS GAS DISCHARGE. TUBE Filed Feb. 21, 1933 Fig.1.

|\\J c Z t INVENTOR K B) %M/ W W HTTORNEY Patented Mar. 12, 1935 UNlTED STATES LUMINOUS GAS DISCHARGE TUBE Leonard Henry Soundy, London, England, as-

signor to Uneon Limited, London, England, a

British company Application February 21, 1933, Serial No. 657,894

In Great Britain 11 Claims; This invention relates to gas-filled electric dis charge and like luminous tubes, and particularly tubes filled with a gas, such as neon, which are employed for luminous signs and advertisements.'

'The invention is especially concerned with a construction of tube and a method of operating same which enables the. tube to be used in a flashing sign, or in other words, which enables the tube to be rapidly extinguished and relighted without any danger of harmful effects due to either breaking a high voltage at the electrodes, or by opening and closing the primary circuit of the transformer used for energizing the tubes, as has been usual previously.

It is well known that in a'gas discharge tube which is supplied with direct current, there is a surface glow upon the cathode, and next to that a dark space known as a Crookes space, then there is a further bright glowing space often referred to as the negative glow, and next a further dark 'spacesometimes called a Faraday dark space, and which is followed by the positive luminous column which extends right to the anode. In a tube supplied with alternating current, and in which, therefore, both electrodes are alternately cathode and anode, these regions occur in the neighbourhood of both electrodes. Now by far the greater part of the voltage impressed across the electrodes is absorbed by the drop in the glow. on the cathode surface, the negative glow, and the two dark spaces, and the fall of potential on the whole of the positive column is relatively small. The present invention aims at producing a flashing luminous tube'in which the positive glow is extinguished, but the flow of current in the regions adjacent the cathode or cathodes is maintained so that the energy and voltage interrupted is only that taken up in the positive column.

Thus, according to the present invention a method of operating a flashing luminous gas discharge tube with direct current or alternating current is characterized in that the flashing is effected by intermittently short circuiting the positive column while the flow of current in the neighbourhood of the cathode or cathodes is maintained, so that the voltage interrupted is only the comparatively small voltage occurring in the positive column.

Examples of construction of a discharge tube in accordance with the invention are illustrated diagrammatically in the'accompanying drawing, in which:---

Figure 1 shows the discharge tube arranged for operation with direct current;

February 29, 1932 (Cl. 176-124) Figure 2 is a cross sectionon the line IIII of Figure 1;

Figure 3 shows the discharge tube arranged for operation with alternating current, and

Figure 4 is an enlarged sectional view of a portion of the discharge tube.

Referring now to Figure 1, the discharge tube a contains the usual cathode b with lead-in wire c. An auxiliary electrode :1 is arranged in the neighbourhood of the cathode b and is connected by a conductor e through a flashingswitch S to the anode j, which is provided with a lead-in wire g. Thus, it will be understood that the positive column between the auxiliary electrode d and the anode f is short circuited whenever the switch device 8 connected to the conductor e is closed. The result is that when the switching device closes, the positive column is extinguished and the discharge takes place between the oathode and the auxiliary electrode, and the dark spaces and the two glowing spaces close to the cathode are maintained when the positive column is extinguished. It will be realized that in a tube arranged according to the invention, the voltage which is to be interrupted is comparatively small, and the total voltage across the electrodes has not to be interrupted. This arrangement enables the tube to be flashed successfully with a simple commercial switch, which has not been possible hitherto, as an elaborate shielded and quenched break usually has to be provided if the circuit is to be interrupted with rapidity.

In the case of operation with alternating cur rent (Figure 3), it is necessary to provide an auxiliary electrode h in the region of the opposite electrode 1. This auxiliary electrode h is connected by means of a conductor k to the switching device 8,- which in turn is connected by the con ductor e to the auxiliary electrode d. With this arrangement, the positive column between the auxiliary electrodes d and h is short circuited each time the switching device closes. In actual practice it is arranged that the positive column occupies as large a part as possible of the total distance between the electrodes and the spaces between the auxiliary electrodes e, k and the main electrodes b, 1 may be shielded from sight. The auxiliary electrodes are placed with the best eflect at the boundary between the positive colum and the Faraday dark space, but they may be placed nearer to the electrodes, either within the Faraday dark space or in the negative glow, or even in the Crookes or cathode dark space. In the latter case, however, they are subject to greater bombardment due to the large potential is no longer a steep potential gradient.

gradient in the cathode dark space and sputtering and ultimate destruction of the auxiliary electrodes are liable to take place in that case.

The auxiliary electrodes are preferably of a finemesh gauze of circular shape, and should be as large in area a" the diameter of the tube will allow. it is found that a convenient size consists in having the circumference of the gauze electrode half way between the circumference of the main electrode and the inner wall of the glass tube.

Although it is stated that a single auxiliary electrode is used in the case of a tube supplied with direct current, and two auxiliary electrodes in the case of an alternating current tube, the invention is not limited in this way. Thus, other gauze electrodes may be placed in various positions along the tube, when any portions of the column may be extinguished in any sequence de sired by suitable switching devices, and the remainder of the tube allowed to remain luminous. In all cases the mesh of the gauze electrode should be fine.

It will be realized that the present invention allows gas discharge tubes such as neon tubes to be flashed rapidly, and a switching device with quite light contacts and no very elaborate insulating arrangements to be employed.

Occasionally it is found that these discharge tubes do not become completely dark when the switch is closed to short circuit the positive column. It is thought that this is due to the fact that the whole of the ions in the gas column are not intercepted by the auxiliary electrodes and that some of them, for example, escape round the edges and maintain a faint discharge through the tube owing to the fact that the gas in the tube is highly ionized at the moment of short circuit, and its resistance is still very small. This drawback is avoided by making the main electrode b comparatively small and almost entirely surrounding it by an insulating body 1 (Figure 4) which enables the discharge onlyto escape through a small aperture m so that a highly localized discharge is obtainedwhich is almost of a point character. The stream from the aperture naturally spreads, but only reaches the outer walls of the tube at some distance from the main electrode. This in itself reduces the tendency of leakage around the edges of the auxiliary electrode d. The latter cannot easily be made to fill the whole cross-section of the tube as otherwise dislocation of the glass wall takes place at the considerable importance in itself, consists in supporting the auxiliary electrode from the insulating casing around the main electrode. In fact, the auxiliary electrode may be supported in an adjustable manner which is of considerable advantage in. view of the fact that it is desirable to be able'to locate the subsidiary electrode accurately in the tube with relation to the Faraday and Crookes dark spaces and at a point where there Thus, a number of axially extending metal supporting rods 12, q may be moulded into the insulating body surrounding the main electrode and the framework surrounding the auxiliary electrodemay be.

secured in an adjustable manner to these rods.

This has the advantage that one of these rods 9 9, qand providing a pair of nuts on each of.

them, one on either side of the framework 11 for the auxiliary electrode d. The whole is mounted at one end of the glass tube and leading-in conductors are taken through separate seals, one fromthe main electrode and the other from one of the supporting rods of the auxiliary electrode.

As will be seen from Figure 4, the main electrode b is comparatively small, and is substantiallya cylindrical metal body made hollow with a central bore 0. It is encased in a flanged moulded casing l of insulating material, such as steatite, dental plaster, porcelain or other readily moulded material which sets hard and'is heat resisting. An aperture 111. of small size is pierced through this casing at the centre of its front surface.

The ionic stream leaves the main electrode b through the central hole m in the form of a conical stream, spreading out and striking the auxiliary electrode d so that when the short-circuiting switch s is closed to connect together the two auxiliary electrodes, the whole of the current passes the short-circuit path, and the positive column in the tube is entirely extinguished.

The main electrode may be of any metal, preferably of iron, aluminum or tungsten and the auxiliary electrode may consist of gauze of any suitable metal such as aluminum, nickel, iron, tungsten, or molybdenum, and may be coated with electron-emitting material.

It will be seen with this arrangement providing a narrow beam, there is no fear of stray ions leaking-past the auxiliary or control electrode between the latter and the glass wall of the tube.

' I claim:-

1. A method of operating a flashing luminous gas discharge tube which consists in starting the tube and intermittently short-circuiting the positive column of the discharge while maintaining current flow through the dark spaces adjacent to at least one of the main electrodes of the tube.

2. In a luminous gas discharge tube, the combination of an envelope, a pair of main electrodes mounted therein, at least one of which is of small dimensions with respect to the cross-section of said envelope, an insulating body substantially surrounding said main electrode of small dimensions but formed with a small aperture in the surface directed towards the opposite main electrode to enable the discharge to escape therethrough to produce a highly localized discharge and a tap electrode spaced from said small main electrode and occupying a major portion of the cross-section of said envelope so as to intercept the greater part of the discharge current.

lope and a tap electrode carried in and filling said insulating frame.-

4. In a luminous gas discharge tube, the combination of an envelope, a pair of main electrodes mounted therein at least one of said electrodes being of small dimensions with respect to the crosssection of said envelope, a frame of insulating material fitting within the walls of said envelope in a position between said main electrode of small dimensions and the main part of said envelope and a tap electrode of metallic gauze carried in and filling said insulating frame.

5. In a luminous gas discharge tube, the combination of an envelope, a pair of main electrodes mounted therein at leastone of said electrodes being of small dimensions with respect to the crosssection of said envelope, a frame of insulating material fitting within the walls of said envelope in a position between said main electrode of small dimensions and the main part of said envelope, a tap electrode carried in and filling said insulating frame, and a body of moulded insulation supported from said insulating frame and surrounding said main electrode of small dimensions on all sides except for a small aperture directed towards said tap electrode. 7

6. In a luminous gas discharge tube, the combination of an envelope, a pair of main electrodes mounted therein at least one of said electrodes being of small dimensions with respect to the crosssection of said envelope, a frame of insulating material fitting within the walls of said envelope in a position between said main electrode of small dimensions and the main part of said envelope, 9. tap electrode carried in and filling said insulating frame, a body of moulded insulation supported from said insulating frame and surrounding said small electrode on all sides except for a small aperture directed towards said tap electrode and separate lead-in conductors to said main electrode of small dimensions and said tap electrode, that to said tap electrode being supported in said insulating frame and said body of moulded insulation.

7. In a luminous gas discharge tube, the combination of a vitreous envelope, a main electrode mounted in said envelope near one end thereof and being of small dimensions with respect to the cross-section of said envelope, a body of insulation surrounding said electrode and furnished with a small aperture directed towards the body of said envelope so as to provide for escape of localized electric discharge, a plurality of supporting rods I extending from said body of insulation towards the body of said envelope, an insulating frame adjustably supported on said rods and a tap electrode carried in said frame, the arrangement being such that the position of'said tap electrode may be accurately adjusted to 'a point where there is no longer a steep potential gradient due to the discharge.

8. In a luminous gas discharge tube, the combination of a vitreous envelope of circular crosssectlon, a main electrode mounted in said envelope near one end thereof, a circular insulating frame fitted within said envelope and located between said main electrode and the discharge space within said envelope, a body of insulation surrounding said electrode and having a small aperture directed towards said frame for the escape of a highly localized electric discharge, a plurality of supporting rods extending from said body of insulation to said frame to support the latter and permit of adjustment of same along said envelope and a tap electrode of metal gauze of fine mesh extending across and carried by said insulating frame. I

9. In a luminous gas discharge tube, the combination of an envelope, a pair of main electrodes mounted in said envelope and arranged for a luminous discharge to be set up between same, a plurality of auxiliary, electrodes arranged in said envelope between said main electrodes to intercept the luminous discharge and a switching device connected to short-circuit the discharge space between any two of said auxiliary electrodes.

10. In a flashing luminous gas discharge tube for direct current operation, the combination of an envelope, an anode and a cathode for setting up the discharge in said envelope, terminals connected to said anode and cathode respectively, a tap electrode located in said envelope between the cathode end of the positive column of the discharge and said cathode, a separate terminal connected to said tap electrode, and a switching device connected between the terminals associated with said anode and said tap electrode for intermittently short-circuiting the positive column of the discharge.

11. In a flashing luminous gas discharge tube for alternating current operation, the combination of an envelope, a pair of main electrodes for setting up the discharge in said envelope, terminals connected to said main electrodes, a pair of tap electrodes located in said envelope substantially one at each end of the zone occupied by the positive column of the discharge, separate terminals each connected to one of said tap electrodes, and a switching device connected between the terminals connected to said tap electrodes for intermittently short-circuiting the positive column of the discharge.

LEONARD HENRY SOUNDY. 

